A polar compound is a molecule with a geometric arrangement of one side carrying a positive charge and the other side a negative charge. Water, ammonia, sulfur dioxide and hydrogen sulfide are examples of polar compounds.
In chemistry, polarity affects a number of physical properties including solubility, surface tension and boiling and melting points. Scientists use polarity to determine whether molecules can mix to become a solution. Polar compounds mix with each other to create solutions. Non-polar compounds also mix with each other, but polar and non-polar compounds do not mix together to create a solution.
Polarity in molecules is created by polar covalent bonds, in which two atoms share electrons to fill their respective valence orbits, creating a positive charge on the side opposite the electrons and a negative charge on the side of the electrons. In water, for example, an oxygen atom shares electrons with two hydrogen atoms. Electrons initially belonging to the hydrogen atoms are pulled toward the oxygen atom, creating a positive charge as the protons from the hydrogen atoms are the most outward-facing part of the molecule on that side. The oxygen atom on the other side of the molecule carries a negative charge, as two additional electrons are pulled toward it to form the covalent bonds.